1. Field of the Invention
This invention relates generally to the field of air filtering for buildings and more specifically to the filtering of carbon monoxide from air.
2. Description of the Related Art
It is undesirable to have carbon monoxide present in the breathable air of commercial or private buildings. However, various small amounts of this poisonous gas are always present since it is produced by automobiles and other industrial processes.
Prior filtering techniques for carbon monoxide have generally required either passing the gas over a catalyst at high temperatures to convert it to carbon dioxide, or else trapping the gas in some sort of absorptive medium. Both of these techniques are undesirable for continuous filtering of building air. The first method requires considerable energy to heat the catalyst material; the second requires frequent replacement of the filter material. A filter with high energy usage and high temperatures is particularly undesirable for a residence where energy costs and safety are both very important. Any filter that requires periodic replacement of its internal parts is undesirable from a cost standpoint. It is also fairly well established that filters that require periodic maintenance may not be well maintained in practice.
Titanium dioxide, along with other materials, is a well known catalyst, and has used been along with a reducing agent, to reduce nitrogen oxides in flue gas (Vogel et al. U.S. Pat. No. 5,225,390). It has also been used as a basis for catalysts that oxidize carbon monoxide and various hydrocarbons (Vorob'iev U.S. Pat. No. 5,204,309). However, to accomplish this, gas temperatures must be higher than 100 degrees C. A typical temperature range is 100 degrees C. to 300 degrees C.
It is known in the art of liquid filtering that titanium dioxide possesses the property of photo-catalytic activity. Here, the titanium dioxide becomes excited by ultraviolet light to act as a very effective catalyst to oxidize hydrocarbons, in solution. A disc of borosilicate glass can be coated with anatase titanium dioxide. Such a reactor can be spun at high RPM in the presence of ultraviolet light while liquids containing photocatalytically degradable organic material are applied to the disk (Urwin et al. U.S. Pat. No. 5,308,458). Dry titanium dioxide has been used to convert ethane to carbon dioxide and water (Daroux et al. Canadian J. of Chem. Eng. vol 63, Aug. 85).
What is badly needed in the field of indoor air quality and HVAC is a low priced passive filter for carbon monoxide in air that works at room temperature and does not become contaminated so as to require periodic replacement or maintenance. This filter should function in a dry state and not require moving parts. It should remove most of the carbon monoxide normally present in breathable air as this air is passed through it at a reasonable flow rate. In addition, the filter should be simple to manufacture.